php - 查询以获取列的差异

Question

我有两个表，主键为“poll_id”，每个表中的列名为“object_id”。 我无法从 t1 获取 t2 中不存在的对象，并且带有 poll_id(主键)。

       T1                           T2

poll_id|object_id            poll_id|object_id
1      | 2                    1     |  2
1      | 3                          |

我需要获取 [poll_id]=>1,[object_id]=>3

Answer 1

使用NOT EXISTS

SELECT poll_id, object_id
FROM t1
WHERE NOT EXISTS
      ( SELECT *
        FROM t2
        WHERE t2.poll_id = t1.poll_id
          AND t2.object_id = t1.object_id
      ) 
  AND poll_id = 1 ;                        -- additional requirement

使用LEFT JOIN/IS NULL

SELECT t1.poll_id, t1.object_id
FROM t1
  LEFT JOIN t2
    ON  t2.poll_id = t1.poll_id
    AND t2.object_id = t1.object_id
WHERE t2.object_id IS NULL 
  AND t1.poll_id = 1 ;                        -- additional requirement

使用NOT IN:

SELECT poll_id, object_id
FROM t1
WHERE (poll_id, object_id) NOT IN
      ( SELECT poll_id, object_id
        FROM t2
      ) 
  AND poll_id = 1 ;                        -- additional requirement